Microstructured optical fibres are known, and can be used for instance for sensing transverse load based on their birefringent properties. An example of such a structure is for instance disclosed in WO2011/061309, which includes a “butterfly MOF” described in relation with FIG. 2.
Another example is disclosed in the paper “Highly Birefringent Photonic Crystal Fibre with Enhanced Sensitivity to Hydrostatic Pressure”, Szpulak M. et al, ICTON 2006, proceedings page 174-177, for instance disclosing a “V-fibre MOF” in relation with FIG. 1C.
Recently, it has moreover been recognised that measuring shear stress or shear load sensing can be performed with Bragg grating-based sensors in microstructured optical fibres, which are embedded in a host material, as disclosed in “Shear stress sensing with Bragg grating-based sensors in microstructured optical fibers”, Sulejmani S. et al., OPTICS EXPRESS 20404, 22 Aug. 2013. The study described herein is based on a “butterfly MOF” structure.
The use of the “butterfly MOF” for shear load sensing as described in Sulejmani S. et al still results in a substantial sensitivity to transverse load, which causes a relatively large cross-sensitivity between the transverse load and shear load, which makes it more difficult to precisely determine the actual level of shear load.
There exists a need for MOF structures which provide an increased shear load sensitivity and selectivity with respect to the prior art structures, and which at the same time limit sensitivity to transverse load when embedded in a host material.